The global warming phenomenon caused by CO2 emission has currently emerged as a social issue. Bio-plastic manufactured from biomass is required to be used in order to reduce the CO2 emission amount. It is known that since CO2, which is generated during a treatment process in which the bio-plastic is decomposed after being used, returns to the growth of the biomass, the bio-plastic does not emit CO2 into the environment at all.
Therefore, the bio-plastic is a polymer material that is very environmentally friendly, and enables to be substituted for petroleum which is a fossil fuel to be depleted someday, and accordingly, research into a technology of preparing a. polyamide resin such as nylon, etc., by using the bio-plastic has been actively conducted.
In the existing method for preparing a polyamide resin by anionically polymerizing a monomer including 2-pyrrolidone, an unreacted monomer is recovered by adding an acid to a refined water to perform neutralization, thereby controlling pH, and distilling a pH-controlled water to induce concentration, wherein a salt is generated at the time of the neutralization, and accordingly, there are problems in that a salt-separation step for separating the salt is separately required, and high energy is needed for the distillation.